The objective of the proposed studies is to characterize the structure and function of platelet activating factor (PAF) isolated from antigen stimulated IgE-sensitzed basophils. Initial studies have indicated that PAF structurally is an alkyl glyceryl phosphorylcholine and we have synthesized a molecule, 1-0-hexadecyl/octadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC) that is physicochemically and functionally identical to PAF. Confirmatory investigations will be conducted to determine directly the structure of PAF by chemical analysis, infrared and mass spectrometry and by gas-liquid chromatography, with particular attention directed towards the chain length of the esterified fatty acid ester in the 2 position. Utilizing AGEPC and various synthetic analogues we will characterize the structure-function relationships of the molecule relating to its potent platelet stimulating activities. Also in vivo studies will be conducted in rabbits to characterize its biologic activities relating to possible intravascular, cardiovascular and respiratory effects.